Hard Doom

Hard Doom is a gameplay mod for Doom and Doom II, built for the ZDoom source port and its derivates (chiefly Skulltag and Zandronum). It was originally created by Aerial, with Matthew Krehbiel (Ghastly) joining the development team a few years after its initial release on November 28, 2008.

Hard Doom was created as a response to the immense popularity of the cooperative and survival game modes on Skulltag servers. Because certain mapsets that offer a reasonable challenge in single player end up being way too easy when playing with multiple people, Hard Doom was conceived as a gameplay mod intended to significantly increase the level of challenge offered by Doom monsters but without deviating too far away from the core gameplay of the game. Hard Doom utilizes several monsters from the Realm 667 beastiary, but many are significantly tweaked from the originals and others are unique creations. The mod also utilizes a series of particle effects and sprite enhancements to give the game a fresh look without straying far from the original visuals.

Due to its challenging gameplay and particular attention paid to balance, Hard Doom is one of the most popular multiplayer gameplay mods on Zandronum. In scope and features, Hard Doom was one of the earliest of such "R667 randomizer" mods, setting the standard that was later followed by other mods such as Complex Doom and Supercharge. The latest version of Hard Doom is 3.8.1, released on October 15, 2018, and the mod is considered to be feature-complete.

Content
By default, Hard Doom utilizes a randomizer system, whereby certain monsters (such as the zombieman) do not always get replaced by the same type of monster, but instead have a chance to be replaced by a common monster - in its particular case: the dual pistol zombie as a common replacement, the sonic railgun zombie as an uncommon replacement, and the rocket launcher zombie as a rare replacement. The random spawners were not present in the earlier versions of the mod, but were added due to popular demand from the playerbase. The developers released version called Hard Doom Lite which does not feature the randomization aspect. Below is a list of the new monsters and weapons that appear in the mod:

New monsters

 * Zombieman replacements:
 * Dual-pistol zombie
 * Sonic railgun zombie
 * Rocket launcher zombie (25 hit points)
 * Shotgun guy replacements:
 * Shotgunner
 * Super shotgunner
 * Quad-shotgun zombie (38 hit points)
 * Heavy weapon dude replacements:
 * Double chaingunner
 * Minigunner
 * Imp replacements:
 * Dark imp
 * Pyro imp
 * Demon replacements:
 * Mauler demon
 * Cyber fiend (200 hit points)
 * Spectre replacements:
 * Lurker
 * Shadow demon (200 hit points)
 * Lost soul replacements:
 * Rictus
 * Visage
 * Cacodemon replacements:
 * Agathodemon
 * Necrodemon
 * Crackodemon (500 hit points)
 * Pain elemental replacements:
 * Pain-elemental
 * Ancient apparition
 * Hell knight replacements:
 * Archon of Hell
 * Hell's Fury
 * Baron of Hell replacements:
 * Bruiserdemon
 * Pyro demon
 * Revenant replacements:
 * Dark revenant
 * Hellfire revenant
 * Mancubus replacements:
 * Daedabus
 * Mafibus
 * Arachnotron replacements:
 * Fusion arachnotron
 * Arachnotron Mk. II
 * Arch-vile replacements:
 * Diabloist
 * Shadowvile
 * Spider mastermind replacements:
 * Spider-demolisher
 * Dark spider-demon
 * Cyberdemon replacements:
 * Cyber-annihilator
 * Dark cyberdemon
 * Wolfenstein SS replacements:
 * SS Nazi
 * Nazi officer
 * Nazi mutant

New weapons
The mod features all the weapons found in Doom II as well as in Skulltag, but these have been tweaked somewhat visually and also in terms of function. It does however also feature two new weapons:
 * Sonic railgun: similar in function to the railgun from Skulltag, this is a rapid-fire weapon that fires yellow railgun projectiles in high succession, but these are much more low damaging than the regular railgun.
 * Quad shotgun: a powerful weapon which packs twice the punch as the standard super shotgun, it can either be fired one burst at a time, or fire its four barrels all at once.